Medical monitoring devices are routinely used in various medical settings to provide crucial data regarding a patient's medical condition. The monitoring devices may be divided into two main groups: monitoring devices that are used to monitor parameters that are a direct measure of one of the patient's physiological functions and monitoring devices that are used to monitor parameters that are an indirect measure of the status of a physiological function. For example, a parameter that is a direct measure for a physiological function is capnography that may be used to measure and provides values of the CO2 concentration in the ventilated breath, which is a direct measure of the patients ventilation functioning. For example, a parameter that is an indirect measurement is blood pressure, which indirectly provides information regarding the functioning of the heart and the cardio vascular condition of the patient.
Capnography is a non-invasive monitoring method used to continuously measure CO2 concentration in exhaled breath. The CO2, which is a constant metabolism product of the cells, is exhaled out of the body, and the concentration of the exhaled CO2, also known as end tidal CO2 (EtCO2), is an approximate estimation of the arterial levels of CO2. The measurements of the CO2 concentration in a breath cycle are performed by a capnograph, and the results are a numerical value displayed also in a graphical format in the shape of a waveform named a capnogram. The numerical value of the results may be presented in units of pressure (mm Hg) or a percentile. The capnogram may depict CO2 concentration against total expired volume, but the more common capnogram illustrates CO2 concentration against time.
Analyzing the capnogram may yield valuable information about the patient's clinical status. A normal capnogram exhibits one or more typical waveforms, each one represents a single respiratory cycle, and deviation from the normal waveform may hint as to the clinical situation of the patient. For example, an abnormally high basal line represents re-breathing of exhaled CO2; a slow increase in CO2 concentration may hint to uneven emptying of the lungs; rising in CO2 concentration without reaching a plateau may hint to situations of asthma or other lower airway obstruction; very small changes in CO2 concentration may indicate an apnea situation, and the like. In addition to displaying respiratory cycles, a trend display is also available in which many individual consecutive breath cycles are compressed together so that changes over time may be easily distinguished, providing yet an additional aid in assessing and monitoring the patient's ventilation and clinical profile.
Capnography is widely used today as an important tool for tracking a patient's ventilation status in various health care settings, such as an Emergency Room (ER), Operating Room (OR), Intensive Care Unit (ICU) and Emergency Medical Services (EMS). Among the clinical applications in which capnography may be used are Cardiovascular (for example in CPR, shock, pulmonary embolism), Respiratory (for example, verification of endotracheal tubing, mechanically ventilated patients, conditions such as Asthma, hyperventilation, hypoventilation, apnea; Sedation (for example during an operation) and/or Patient transport (both intra- and inter-hospital).
In addition to CO2 concentration, various other parameters may be indicative (directly or indirectly) of the ventilation (respiratory) status of a patient. Such parameters may include, for example, saturation of oxygen in the blood cells and other organs, heart rate, respiration rate, breath flow rate, blood pressure, and the like. Combinations of various parameters may yield an improved indication of the clinical condition of the patient, in general, and of the ventilatory status of the patient, in particular.